Activation of Acceptors in Mg-Doped, p-Type GaN
- PDF / 430,447 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 40 Downloads / 209 Views
with a low temperature GaN buffer layer. After growth, these films were semi-insulating with resistivities of >107 0 cm at 500 K. The samples were not initially exposed to any post-growth acceptor activation processes. The incorporation of Mg was verified by secondary ion mass spectrometry (SIMS). The SIMS depth profiles revealed a uniform distribution of Mg throughout the film at a concentration of -6x 1019 cm 3 . The GaN films were annealed in a RTA system under flowing N 2. The heat-up time to the annealing temperatures was -5 s and temperature overshoots were minimized (< 3 K). The hydrogenation was performed with a remote microwave plasma operating at 2 torr [7]. The Hall measurements were conducted in the temperature range from 80 K to 500 K. The magnetic field was 17.4 kG. Samples of 5 x 5 mm2 size were cut and metal dots were vacuum evaporated in the four corners to obtain ohmic contacts in the Van der Pauw geometry. For the PL measurements, the samples were mounted in a cryostat and immersed in liquid He to achieve a sample temperature of -2 K. The PL spectra were excited with the 325 nm line of 30 mW HeCd laser with a pumping power of -1 W / cm2. The resolution of the spectra was 0.05 nm. ACTIVATION OF ACCEPTORS The as-grown, Mg-doped GaN films exhibited high resistivity, and reliable resistivity measurements could only be obtained at elevated temperatures [8]. After annealing at 500'C, the resistivity of the sample remained basically unchanged (-_107 Qcm at 500 K). After the annealing temperature was raised to 775°C, the resistivity reaches a value of - 3 Qcm at 300 K.
1019
(a) Temperature (K) 500 200 150 ,, , ,300 , ,
S
10
..
.
p-type GaN:Mg RTA: 7750C, 5 min
1018 E
(b)
S10
17 1016
"
E >,
o
-
U
0
o0
mm.
1015 0) o-r
0
1014 1013
2
3
4 5 6 7 1000/T (1/K)
1 102
8
103 Temperature (K)
Fig. 1.Hole concentration (a) and hole mobility vs temperature (b) as determined from Hall effect measurements. The symbols refer to experimental data and the solid line in Fig. la is calculated using the charge neutrality condition. The solid line in Fig. lb indicates a temperature dependence of -T' L4 of the hole mobilities at high sample temperatures. 596
Hall effect results after annealing at 775°C are shown in Fig. 1. Figure 1a and b show the hole concentration and the hole mobility, respectively, as functions of the sample temperature. The hole concentrations p were obtained from the experimental Hall constants RH with p = rH/qRH (q = electronic charge); the Hall scattering factor was assumed to be isotropic, temperature independent and of unity value (rH =_ 1). The temperature dependence of the electron concentration shown in Fig. l a reveals activation by a shallow acceptor only for temperatures above 200 K with impurity band conduction at lower temperatures. The solid line in Fig. ] a is calculated from the charge neutrality condition. The model assumes a single acceptor species (Mg(ja), specified by its thermal activation energy and uniform bulk concentration, and partial compensation by a
Data Loading...
